There are a variety of manufacturing processes that require tight tolerances and part quality control. One example is the wire harness industry where wire stripping and crimping operations must be accurate to achieve appropriate and acceptable end products. Another example is the tubing industry and in particular the tubing industry that is related to fluid systems on automotive vehicles.
Typical automobile fluid systems include many tubes and hoses. Example systems include the brake system, fuel system, cooling system, steering system, air conditioning system, among others. Each of these systems handles a specific fluid and typically must operate in a relatively wide range of pressure and temperature conditions. Each of the systems has certain operating parameters that must be met to achieve adequate system operation over the life of the vehicle.
It is important, regardless of the specific system, that the fluid system junctions are 100% reliable for as long as possible. In most instances, the tubes are formed to have a specifically designed end to establish a connection with another portion of the fluid system. The ends of most of the tubes are specially formed to ensure that there are no leaks in the system, even under extreme pressure conditions. In some examples, a hose may be crimped over a formed tube end or the tube may be fastened using a nut compressing a flared end to a mating fitting. In almost all instances, the connection between the tube and the other portion of the fluid system requires the tube end to be specifically and properly formed for that specific purpose. The integrity of the overall fluid handling system depends upon many such tube ends.
Conventional manufacturing processes include forming tube ends using pressing operations on machinery. Appropriate tooling is selected to apply an appropriate amount of force to the raw material to establish the desired end configuration for the tube. A variety of presses and tooling for accomplishing such manufacturing are common.
One method of ensuring appropriate part quality is to inspect the tube ends after the parts are made. This approach has limitations in that it is time consuming, labor intensive and introduces an additional step during the manufacturing process, which reduces the economies of the overall process.
It has not been possible to achieve appropriate measurements during the forming process to obtain part quality information simultaneous with the formation of the parts. One barrier to such an approach has been that it is difficult to obtain a reliable force measurement signal utilizing known force measurement technology. In the wire harness field, for example, a sensor is situated “in line” with the load and is exposed to full load forces. Tube forming processes, however, include peak forces, vibration, speed and other physical factors that make it impractical or not cost-effective for using traditional load sensors for such an application. Additionally, the machine design, variety of machines and the lubricants involved with such machines render traditional sensing arrangements unuseful for the tube end forming process.
Another factor that has contributed to the inability to adequately measure part quality during a tube end forming process is that many tubes have a coating or jacket on an outer surface of the tube. Such coatings or jackets assist in the eventual fluid system reliability, however, they interfere with the ability to accurately measure and compare forces used during end forming operations. Depending on the thickness and integrity of the coating, for example, the forces applied during an end forming operation may appear different because of the coating, which has no necessary connection with the quality of the formed end. Direct peak force measurement is not useful where a tube has a jacket of coating material because a defect in one area may be compensated for by another defect in an unrelated area. For example, a tube with a reduced wall thickness should appear to fail a test, but may pass an inspection test if the coating material was not appropriately stripped in that area such that the coating caused the measured peak force to be inaccurate compared to what it would have been if just the thin-walled metal were present.
There is a need for an improved arrangement that allows for monitoring part quality during a tube end forming process. This invention addresses that need while avoiding the shortcomings and drawbacks of previous attempts.